Firebase - Firebase is a cloud service designed to power real-time, collaborative applications for mobile and web.
Parse (Updated) - Parse with five new products, live from F8
Back4App - For devs, by devs. An easy way to build, host and manage Apps using the open source Parse Server. Scalable Servers, Pre-build examples, Cross-Platform support
Kumulos - Made for the business of mobile app development, Kumulos helps you manage the commercial and technical performance of Apps, so you drive a better outcome for your clients.
Azure Mobile Apps - Build engaging cross-platform and native apps for iOS, Android, Windows or Mac with Azure's Mobile App Service.
CouchBase - Document-Oriented NoSQL Database